Because of requirements for water conservation, low flow drip systems have become an important means of watering plants and the like. These drip systems, along with home use applications, require flow rates down to one (1) or two (2) gallons per hour. Present 0.75 inch inlet port sprinkler valves are suitable for flow rates from five (5) gallons per minute up to thirty (30) to forty (40) gallons per minute. These present valves require flow control adjustment means, large compression shut-off springs, and solenoid return springs. The prior art devices balance fluid pressure on a single diaphragm against a variable spring force.
The prior art diaphragm closing springs and solenoid springs must be of sufficient strength to offset normal internal valve fluid pressures of 40 psi to 150 psi.
Further, fluid flows in the prior art solenoid circuits whenever the valve is in the "ON" state. This continual flow of fluid in the small orifices and passages of the prior art solenoid circuits may cause a problem if there is sediment in the fluid.